The present invention relates to an inkjet printer that ejects ink on a recording medium to print an image thereon.
Conventionally, a so-called serial type inkjet printer has been known. In the serial type inkjet printer, an inkjet head is mounted on a carriage that reciprocates in a direction perpendicular to a feeding direction of a recording sheet (i.e., in a width direction of the recording sheet). A tube is connected to the inkjet head for supplying ink from an ink supplying source to the inkjet head. When an image is printer using such a serial type inkjet head, when the carriage changes its moving direction, a large acceleration acts on the inkjet head and the ink inside the tube, which connects the inkjet head with the ink supplying source. The acceleration generates dynamic pressure in the ink within the tube.
Some inkjet head is provided with a sub-tank, which is also mounted on the carriage. When the sub-tank is provided, the ink inside the sub-tank is ruffled to be frothed. Then, the ink may entrains bubbles. Due to the dynamic pressure and/or entrained bubbles, the inkjet head may eject the ink unstably.
An example of a structure to overcome the problems mentioned above is disclosed in Japanese Patent Application Provisional Publication HEI 10-329330. The inkjet head disclosed in this publication employs a sub-tank having an ink chamber which is divided with a divider into a first ink room and a second ink room. The first ink room is in fluid communication with an ink cartridge through a tube, and a second ink room is in fluid communication with an inkjet head. An opening is formed on the divider at a lower end thereof to connect the first and second ink rooms. Further, on side walls of the first and second ink rooms, openings closed with air shielding elastic films are formed.
In the above-mentioned sub-tank, the variation of the pressure of the ink can be absorbed with the deformation of the elastic films, and while bubbles introduced into the first ink room will not flow into the second ink room.
However, in the inkjet printer disclosed in the above-described publication, the divider of the sub-tank is formed so that it extends parallel to the reciprocating direction of the carriage. Therefore, the divider cannot prevent the ink in the sub-tank from being ruffled by the reciprocating motion of the carriage. Therefore, the ink in the sub-tank (in the second ink room) may froth up and the bubbles entrained in the ink may flow from the second ink room into the inkjet head, which makes the ink ejection of the inkjet head unstable.